The invention described herein may be manufactured and used by or for the government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
1. Field of the Invention
The present invention relates to a solid-state apparatus for tracking the wavelength of a laser emission. More particularly, the apparatus uses a 3xc3x973 coupler to determine the frequency shift of the laser emission.
2. Brief Description of the Related Art
Currently available tunable lasers can cover hundreds of nanometers of continuous tuning on the 1550 nm communications wavelength band. Knowing the precise wavelength at any given time can be extremely difficult. Typically, this measurement has been achieved using a Fizeau wavemeter. These instruments are effective, but they require careful alignment and sophisticated processing of the optical signals.
U.S. Pat. No. 5,798,521 to Froggatt discloses a long Michelson interferometer, constructed from fiber-optic devices, that provides an excellent means of measuring small changes in wavelength to a very high degree of precision. This patent, however, does not determine the direction of the wavelength change, and, as a result would fail if the tuning direction changed. Although most laser sweeps are monotonic, the required retrace, and the drift in wavelength while the laser is not being tuned are not necessarily monotonic.
The present invention includes a solid-state apparatus for tracking the wavelength of a laser emission comprising a guided wave directional coupler having at least three inputs and three outputs constituting channels, wherein any phase shift induced between the channels is substantially unaffected by changes in the wavelength over the intended range of operation, means for passing a portion of a laser emission through two substantially different path lengths, wherein the laser emission exiting from the two substantially different path lengths are recombined using the directional coupler, means for detecting the power level in at least two of the outputs of the directional coupler and means for determining the direction and magnitude of laser emission wavelength changes from changes in the at least two detected power levels.
The present invention further comprises a method for tracking laser emissions, comprising the steps of providing a solid-state apparatus for tracking the wavelength of a laser emission having a guided wave directional coupler having at least three inputs and three outputs constituting channels, wherein any phase shift induced between the channels is substantially unaffected by changes in the wavelength over the intended range of operation, means for passing a portion of a laser emission through two substantially different path lengths, wherein the laser emission exiting from the two substantially different path lengths are recombined using the directional coupler, means for detecting the power level in at least two of the outputs of the directional coupler and means for determining the direction and magnitude of laser emission wavelength changes from changes in the at least two detected power levels, initiating a laser emission into the apparatus, splitting the laser emission into differing phase shifts and processing the phase shifts sufficient to track the laser emissions.
Additionally, the present invention includes a tracked laser emission product by the process comprising the steps of providing a solid-state apparatus for tracking the wavelength of a laser emission having a guided wave directional coupler having at least three inputs and three outputs constituting channels, wherein any phase shift induced between the channels is substantially unaffected by changes in the wavelength over the intended range of operation, means for passing a portion of a laser emission through two substantially different path lengths, wherein the laser emission exiting from the two substantially different path lengths are recombined using the directional coupler, means for detecting the power level in at least two of the outputs of the directional coupler and means for determining the direction and magnitude of laser emission wavelength changes from changes in the at least two detected power levels, initiating a laser emission into the apparatus, splitting the laser emission into differing phase shifts, processing the phase shifts sufficient to track the laser emissions and calibrating the laser emission.
The present invention is particularly suited for using a 3xc3x973 coupler, and detecting a wavelength change to a precision of from about 0.1 xcexcm or less.